ROLE OF SIF PROTEIN IN SYNAPTOGENESIS

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We are interested in understanding the molecular mechanisms that regulate synaptogenesis. To approach this issue, we have employed genetics of Drosophila and screened mutant flies that show reduced locomotor activity at the adult stage. One of the mutant strains idetified during this screening is still life (sit), which was later found to encode a gulanine nucleotide exchange factor that specifically reacts for Rac1 in vitro. Interestingly, this protein was found to localize at the submemebraneous regions of the periactive zones that surround the active zones in the synaptic terminals. The goal of this project is to reveal the in vivo function of SIF protein in the synaptic terminals by analyzing the sif mutant animals.Our genetic screen to 9000 chromosomes treated with ethylmethane sulfonate, a chemical mutagen, successfully identifed more than 10 sif mutant alleles. Western blotting and sequencing analyses further revealed that 2 of them have terminal-codon mutations, each causing functional null. These mutant animals are not homozygously lethal but show reduced locomotor activity. We have not so far succeeded in identifying clear morphological phenotypes at both light and electron microscopic levels. It is however possible that sif may be involved in refinement of synaptic arborization that occurrs during synaptogenesis or responding to neural activity. To test this hypothesis, we have tried to visualize a small number of neurites in the adult brain using GFP and to find any effects of sif mutation on their morphology.